The present invention generally relates to check valves. More particularly, the present invention relates to swing check valves including a flapper disc in combination with a spring assembly.
Check valves having a closure mechanism consisting of a resilient disc are commonly used in the water and waste water industry to prevent reverse flow in such systems. Typically, these resilient disc check valves have a disc that is mounted within a valve body at a forty five degree angle with respect to the flow path when in the closed position. The disc includes a hinge which is typically integrally molded to the disc and rigidly held in place in the valve body. The resilient disc typically pivots about thirty five degrees to an open position to provide a full flow area or near full flow area. The thirty five degree span of movement is preferred because it provides a short closing stroke which avoid a slamming of the valve in a closed position.
A spring has been used as a return element and are desirable because it prevents the occurrence of valve slam and water hammer by biasing the disc into the closed position before the flow reverses in the pipe. In contrast, if the flow reverses in the pipe before the disc is in the fully closed position, the reverse flow will slam the disc into the seat and violent forces within the pipe and noise will result. The sudden stoppage of the reverse flow can cause the phenomenon known as water hammer in the pipe. Spring return mechanisms are often provided with resilient check valves. Also, pumping applications with high head, surge tanks or multiple pumps have long proved a challenge to operators trying to minimize line surges resulting from slamming check valves. The surge force or water hammer is proportional to the pipe flow velocities and the resulting reverse flow. For example, every one foot per second change in flow velocity theatrically creates a line pressure surge of fifty-four pounds per square inch (“psi”) above the static system pressure. However the currently available spring mechanisms are not easily removeable, cannot be fine-tuned in the field, arecostly to fabricate and do not minimize friction loses caused by the hydraulic conditions.
Thus, a need exists for an adjustable spring closing mechanism to close a check valve to minimize the damage caused by the reverse flow and reduce the pipe line surge or water hammer.